The accordion is a free-reed aerophone musical instrument consisting of two keyboards, one for the melody and the other for the accompaniment. The keyboards have their own wooden sounding board and are joined by bellows in the middle that produce the air stream which makes there eds vibrate.
The reeds are thin strips of harmonic steel which, fixed at their base to a supporting metallic plate, become "voices", i.e.the sources for the sound of the instrument. The "voices" can produce sound individually or in conjunction with other voices of the same note, so that we may have sounds in 2 ^, 3 ^, 4 ^ or 5 ^, depending on the chosen tone. The fifth register reproduces the deep and full-bodied voice of the organ.
Besides issuing different tones, the registers, which are controlled by special key pads, are also aimed at extending the sound possibilities beyond the canonical 3.5 octaves ca.
The Accordion, working as a miniature orchestra, is able to interpret also the great music thanks to separate keyboards, which allow to govern both the melody and the bass keys. More over the bellows, in addition to providing the necessary pressure for the vibration of the reeds, has a very sensitive structure granting to the player a potential for high expressivity.
The ancient Accordions - renamed "organetti" in Italy - operated a diatonic musical scale and are the ancestors of the modern accordion ("fisarmonica" in Italian). They witness the evolution ofthe instrument until the year 1890, when Mariano Dallapè, in his factory in Stradella, ended the experimental phase by applying to both keyboards the chromatic musical scale. In the same year, he codified the bass keys inpre-established chords - called Stradella Bass system - which could constituted the ideal accompaniment to all kinds of music in all keys. From that time on,the accordion was considered at the same level as the classical instruments,because able to interpret the great scores of the past. Thus ended the substantial evolution of the "sound box" , whose following history was characterized by minor improvements in functionality.